The invention relates generally to static structures and more particularly to a reinforced concrete bridge or culvert structure having parallel side walls interconnected by a planar horizontal top span and an open bottom.
Accompanying the development of motor vehicles and roadways designed to permit their movement rapidly and expeditiously between two points has been a similar development relating to smooth and level passage across various obstructions such as ditches, creeks, rivers and other roadways. Such structures can vary from one foot diameter pipes to suspension bridges. In what might be characterized as the smaller half of this spectrum of designs are found circular and elliptical concrete culverts, corrugated metal culverts, box culverts, concrete and metal arches and bridges constructed of conventional steel I-beams and poured, reinforced concrete, to name the more common approaches. Each such design includes features and confers benefits which make it particularly suitable for certain applications but also suffers from detriments and disadvantages which limit or prevent their utilization in other circumstances.
Precast or prefabricated construction is attractive from cost and assembly standpoints. Since such designs are typically cast in significant numbers at a single manufacturing site, the cost per unit is relatively low. Transportation to the job site, in most instances, is readily achieved by truck or rail cars and assembly is equally straightforward since dimensional tolerances are generally closely held by the casting process. Such structures, particularly the larger sizes and those fabricated of corrugated metal, however, do require carefully and properly compacted backfill in order to achieve their rated load carrying capacity. The backfill is an important consideration of the installation of the structure and must be carefully performed. These structures may also be susceptible to wash out by water flowing around the outside of the culvert and eroding supporting soil. A problem similar to that experienced with improper backfill can thus result due to the lack of appropriate support about the culvert subsequent to soil erosion.
Many of the foregoing difficulties are not shared with bridges and culverts which may be characterized as an arch type. Here, a curving, arched plate forms the upper portion of the bridge or culvert and is supported by appropriately placed footings at each end of the arch plate. In such installations over water, such as creeks and rivers, the water remains in its natural watercourse and thus erosion problems are minimized. Footing construction in this design is somewhat critical, however, since significant outward as well as downward forces must be borne by them.
A problem such arch designs share with circular and elliptical culverts however relates to internal useable height versus total height of the roadway supported by the structure. First of all, if a bridge or culvert supports a roadway over flowing water, such structure must provide for a maximum design flow which will increase the overall diameter and height of the structure in accordance with maximum predicted flow requirements. Given the curved nature of such a structure, at any location in an arch and in the upper half of an elliptical or cylindrical structure, rising water flow levels must pass through a steadily reducing flow region. Thus the overall flow area of the structure and its height must be greater than what such dimensions would be if the structure were rectilinear. Secondly, and perhaps more importantly, such devices, as noted above, require backfill and cover which can increase the height of the supported surface over the watercourse or other obstacle by several feet. The necessity for cover may thus substantially increase the overall cost of the bridge or culvert installation since approaches on either side must then frequently be constructed in order to raise the surface of the roadway smoothly and evenly to the maximum height of the overpass from the surrounding terrain.
Various concrete and corrugated metal culverts, bridges and arch bridges are known in the prior art. Typically, concrete culverts include a plurality of abutting sections such as disclosed in U.S. Pat. Nos. 1,130,508 and 1,184,634. Reinforcing bar is commonly used in such concrete devices as disclosed in U.S. Pat. Nos. 1,412,616 and 1,860,533. Structures which may be generally categorized as rectilinear have also been suggested in the prior art. Various configurations with integral catch basins such as disclosed in U.S. Pat. No. 1,870,156 or culverts constructed of sections of concrete slabs as shown in U.S. Pat. No. 1,662,714 are known. Arch constructions are disclosed in U.S. Pat. Nos. 3,482,406 and 4,211,504, the latter being fabricated of corrugated metal. Generally, each of the designs disclosed in the foregoing patents is subject to at least one of the requirements or drawbacks delineated above with regard to prior art devices generally. This suggests that improvements in the design of concrete culverts and bridges can be made.